Highly active facet-controlled nanocatalysts deteriorate readily via surface-atom migration during their use. This study develops a method for regenerating a degraded facet-controlled nanoparticle catalyst by reorientation of surface crystalline structure via the dissolution-reprecipitation process using an organic modifier. The supercritical hydrothermal treatment with the carboxylic acid modifier changes the CeO2 nanoparticles morphology to cubic-like over time to expose the (100) facet. This morphological transformation dynamics suggests that the modifier not only stabilizes the (100) facet but also accelerates the dissolution-reprecipitation process, promoting facet modification and catalyst regeneration. The facet-controlled nanocatalyst regeneration is verified experimentally by the recovery of oxygen storage capacity in the CeO2 nanoparticle, which is an indicator of the catalytic activity.